Method and device for grinding central bearing positions on crankshafts

ABSTRACT

An apparatus for grinding center bearings of crankshafts includes a clamping unit for clamping and driving a crankshaft; a grinding spindle, positionable perpendicular to the crankshaft; a plurality of grinding wheels on the grinding spindle, corresponding to the number of center bearings to be ground; a plurality of steadies, for supporting the crankshaft, opposite the grinding spindle; and an additional processing unit for performing preliminary grinding on the center bearing, by forming an elevated bearing seat for the steadies, opposite the bearing, such that the steadies are continuously guidable during grinding of the center bearings. In a method for grinding center bearings of a crankshaft using the apparatus, the center bearings are simultaneously ground using a multilayer grinding wheel set, and prior to a final grinding of the center bearings to their final dimensions, a bearing seat for a steady is ground on at least one center bearing.

The present invention relates to an apparatus for grinding centerbearings, specifically of crankshafts and to a method for performingsuch grinding.

There are a number of options available for performing grinding ofcenter bearings or main bearings of mass-produced crankshafts.

For instance, the center bearings can be ground by means of individualgrinding wheels, which however is associated with substantially highergrinding time because each main bearing is processed individually.Furthermore, a relatively complex machine design is required in order toensure flexibility for such a grinding process.

Furthermore known, but not very common in mass production, is processingthese bearings on the crankshafts by means of so-called “centerless”grinding.

The most widely used method in mass production is so-called multilayergrinding, in which a plurality of grinding wheels of one grindingspindle simultaneously come into contact with the crankshaft at theaforesaid locations of each main bearing. The machines employed for thishave been known for some time and have a design such that an adjustingunit is constructed on a machine bed by means of a grinding spindle anda dressing apparatus. The dressing apparatus preferably moves into placelinearly in the direction of an axis that runs transverse to the mainaxis or center axis of rotation of the crankshaft. Arranged in theregion in front of such a grinding machine is a grinding table that iseither installed fixed on the machine bed or can be moved by means of acomputer numerically controlled (CNC) axis in the direction of an axisthat runs transverse to the adjusting axis and parallel to the axis ofrotation. Installed on this grinding table are a workpiece spindle headand a tailstock, whereby the workpiece spindle head contains theworkpiece spindle. The workpiece spindle acts in a known manner toreceive a chuck or a carrier for the crankshaft. The tailstock islikewise installed on the grinding table and is manually displaceablefor adjusting to various lengths of the crankshaft. A tailstock sleevecan be moved forward and backward automatically for loading andunloading the crankshaft, as is generally known for conventionalcylindrical grinding machines.

There are two options for clamping the crankshaft, which occurs on thespindle head side: either a floating carrier system or center clampingchucks. The workpiece spindle head and thus the crankshaft are caused torotate by means of a motor. The tailstock sleeve is provided with acorresponding countertip that in general is embodied as a so-calledstanding tip. The crankshaft is then received between these tips at itscenter between the workpiece spindle head and the tailstock sleeve,which ensures that the center axes of the workpiece spindle and thetailstock sleeve are precisely aligned with the center axis, i.e., axisof rotation, of the crankshaft.

For precisely monitoring the grinding process, the workpiece is measuredin real time during grinding by means of two measuring devices and themachine is correspondingly corrected.

As a rule, aluminum grinding wheels are in widespread use in thedescribed multilayer grinding method, in particular in crankshaftproduction. These machines are characterized in that they have a wearamount of approx. 1,100 to 600 mm in the grinding wheel diameter. It canbe assumed that dressing must be performed after every 20 to 30crankshafts ground and the dressing amount will be on the order ofapprox. 0.03 mm.

In the multilayer grinding method, it is advantageously possible togrind center bearings or main bearings that have lateral undercuts, thatis, no face sides are ground. In addition, it is also possible to alsogrind main bearings with lateral radius transitions to this face side aswell as the face side to this main bearing with a height of approx. 4 to5 mm.

Grinding of such main bearings with lateral radius transitions and anyface sides proves to be substantially more difficult, since in this casethe method is much more critical in terms of the grinding technologyused.

Furthermore, with the multilayer grinding method on crankshafts, it isalso possible to perform grinding of its center bearings or mainbearings with or without lateral radius transitions and any face sides,as well as grinding center sections on the flange or journals, wherebyhowever no face surfaces are ground at the same time on these centersections of the flange and journals.

Depending on the size and design of a crankshaft to be ground, thesteadies are employed during grinding for support thereof, especiallywhen grinding with aluminum grinding wheels, due to the grindingpressure on the crankshaft generated by the grinding wheel.

This problem of elevated grinding pressure with associated highercutting forces also occurs with so-called cubic boron nitride (CBN)grinding wheels, since increased metal must be removed with them inorder to make the grinding process economically feasible in general.However, this is not entirely due to the required clocklime, whichshould be achieved in a desired manner, but is also due to theproperties of the CBN grinding wheel itself. CBN grinding wheels,preferably those that are ceramic bound and have a coating height ofapprox. 5 mm, have the advantage that they can be operated at anincreased cutting volume, but they also suffer from the disadvantagethat the cutting forces are higher due to the specifications of thegrinding wheels, whereby the entire grinding process becomes technicallysubstantially more difficult.

However, a major advantage of grinding with CBN grinding wheels is thatthey can be operated at increased cutting volumes and that the dressingcycles increase approximately ten-fold, which means that the overallproduction and non-production times spent on finishing one crankshaftare substantially lower. This makes possible increased output ofcrankshafts per unit of time.

Employment of such CBN grinding wheels is desirable, but the increasedgrinding pressure during grinding renders initial grinding of thecrankshaft in the region of a main bearing, at least up to the placementof the support steady during grinding, particularly problematic in termsof grinding technology.

Given these considerations, it is the object of the present invention todevelop a method and an apparatus that represents a substantialimprovement in terms of grinding the steady seat.

This object is achieved with an apparatus in accordance with thefeatures of claim 1 and with a method in accordance with the features ofclaim 8.

Fundamentally, when grinding the steady rest it is very important that,first, it runs very true with respect to the main bearing to be ground,and, second, it has very good roundness in this respect.

In accordance with the invention, therefore, the apparatus isdistinguished in that provided for preliminary work at least on onecenter bearing of the crankshaft is an additional processing unit thatis provided for the bearing seat for placing a steady for the finalprocess of multilayer grinding.

Preferably the processing unit is an additional grinding unit with atleast one grinding wheel for grinding processing of the center bearingof the crankshaft provided for the steady bearing seat.

In this case it is advantageous when the at least one grinding wheel ofthe processing unit has a narrower width than the width of the centerbearing so that the ground running track created for the steady on themain bearing is wide enough that the steady jaws can be placed with noproblem. The ground running track that is produced by the narrowgrinding wheel must be at least approx. 2 mm wider than the steady jawsthemselves. This process is used primarily when the main bearing must beground with corner radii.

In accordance with the invention, the additional processing unit caneither be moved into place toward the crankshaft or pivoted into placeif the grinding wheel is situated in a non-contact position with thecrankshaft for the final multilayer grinding of the crankshaft.

In accordance with the invention, multilayer grinding is performed suchthat, prior to grinding the center bearings to their final dimensions,at least the bearing that will act as the bearing seat for a steady ispre-ground. That is, all of the processing steps are performed with theworkpiece clamped.

In accordance with the invention, there are two fundamentally differentoptions for this. When grinding main bearings with lateral undercuts inwhich the face side of the main bearing is not also ground, theprocedure is possible without using a so-called additional grindingdevice, as described in the foregoing in connection with the inventiveapparatus. In this case it is necessary that an elevated contour remainson the main bearing of the crankshaft during preliminary processing bymean of rotational milling or turning so that then during subsequentmultilayer grinding in a grinding machine for multilayer grinding thiselevation is first ground off. The elevation must be at least the widthof the steady seat to be produced, whereby this elevation must alreadybe ground clean before an adjacent main bearing is processed with thegrinding wheel set. In other words, optimum values can also be achievedhere with respect to the required accuracy in terms of trueness of theruns and roundness. Then the steady is placed on this ground runningtrack and subsequently the grinding wheel set of the grinding spindle ismoved into place and the main bearing or bearings are ground until theyare finished.

Another option is to begin grinding the steady seat by means of agrinding wheel as described in the foregoing in connection with theapparatus, whereby an additional grinding device is employed within thegrinding machine.

In both cases, in accordance with the invention the steady is alwaysguided for smooth counterbearing while the bearing undergoes multilayergrinding to its final dimensions, whereby measuring devicesautomatically measure the crankshaft during the process so that thegrinding process can run practically identical to grinding with thealuminum grinding wheel.

The method/apparatus in accordance with the invention described in theforegoing are explained in greater detail in the following using theexemplary embodiments illustrated in the drawings.

FIG. 1 is a schematic top view of a grinding cell of the inventiveapparatus while grinding the steady seat;

FIG. 2 is a simplified schematic side elevation for illustrating thearrangement of the individual grinding wheels;

FIG. 3 is a schematic top view during multilayer grinding of thecrankshaft;

FIG. 4 is a simplified schematic side elevation with the additionalgrinding device outwardly pivoted;

FIG. 5 is a contact by the grinding wheel while grinding with bearingswith lateral radii; and,

FIG. 6 is grinding of a steady seat at a bearing with pre-processedelevated running track.

FIG. 1 is a simplified representation in the form of a top view, wherebya crankshaft 1 is illustrated with the clamp and grinding wheel set 12,13. The crankshaft 1 is received in a floating chuck 6 with a tip 8 inthe center of the crankshaft 1 and is positioned longitudinally by alongitudinal stop 7.

The floating-borne clamping jaws of the chuck 6 clamp the crankshaft 1at its flange so that it provides radial travel for grinding.

The crankshaft 1 is also received by a centering tip 9 on the side ofthe tailstock so that the crankshaft 1 is received and clamped at bothends in its centerings, which have already been processed, whereby it ispositioned precisely for grinding in terms of position and clamping.

Furthermore illustrated are the measuring devices 4 and 5 installed onthe grinding table; however, these do not come into contact with thecrankshaft during grinding of the steady seat.

The steady 3 is also installed on the grinding table, but duringgrinding of the steady seat it necessarily does not have its jaws on theworkpiece.

The crankshaft 1 has a plurality of main bearings 15, namely in thepresent example I, II, III, and IV. Grinding of the steady seat occursin the illustration shown in FIG. 1 at the center rotating main bearingII.

For this, a processing unit 11 in the form of an additional grindingunit is employed that is preferably embodied with a spindle unit in theform of a motor spindle. This motor spindle in its front region at itsspindle nose receives a grinding wheel 10.

In order for this additional grinding device 11 to be able to be pivotedto the crankshaft, it must stand parallel to the Z axis, which the CNCaxis of the grinding table represents, and the grinding wheels 13 mustbe moved out of the way by means of the X axis, which moves the grindingspindle head 12 into place.

In order that the crankshaft 1 does not have to be moved in thedirection of the X axis, during grinding of the steady seat thisadditional grinding device 11 is pivoted such that the narrow grindingdisk 10 is arranged for grinding the steady seat largely centered infront of a grinding wheel 13 of the grinding wheel set of the grindingspindle 12. The X axis, which moves the grinding spindle head, uponwhich the additional grinding device 11 is also installed, is used sothat the grinding wheel 10 can be moved to the crankshaft.

FIG. 1 furthermore illustrates the grinding spindle 12, which has acenter axis 14 that runs exactly parallel to the crankshaft, about whichthe grinding wheels 13 are rotatable for processing the main bearings Ithrough IV.

The main bearings on the crankshaft 1 that are to be ground are labeled15.

In order to keep the cutting pressure during grinding of the steady seatas low as possible, the grinding wheel 10 has a width of approx. 10 to12 mm, whereby the steady jaws are for instance approx. 8 mm wide. Agrinding wheel made of aluminum or a CBN grinding wheel, for instance,can be employed for grinding means for grinding the steady seat.

In the present example the additional grinding device 11 is described asa pivotable unit. However, it is also possible either to drive or pivotthis additional grinding device 11 to any position within the grindingmachine.

FIG. 2 is a highly simplified side elevation in the region of the mainbearing II in FIG. 1. The grinding wheel 10 for grinding the steady seatis arranged in front of a grinding wheel 13 of the grinding spindle 12.The crankshaft 1 is shown in section. As can be seen, the center axes ofeach of the grinding wheels 10 and 13 and the center axis of thecrankshaft 1 are parallel, whereby these center axes are preferably inone horizontal plane.

FIG. 3 now illustrates the final process in multilayer grinding of thebearings I through IV, whereby these are now ground simultaneously. Thisis necessary since all of the grinding wheels 13 are received on thegrinding spindle 12, which is borne bilaterally. The grinding wheel setis moved into position by means of the X axis, CNC controlled. Duringthe multilayer grinding now, the jaws of the steady 3 are placed on themain bearing II so that the workpiece is very well supported during thegrinding process. In order to attain exact diameters of the mainbearings on the crankshaft 1, preferably one diameter-measuring head 4and 5 is placed at each of the main bearings I and IV. During grinding,the crankshaft 1 is continuously monitored with respect to target andactual measurement. Corrections then occur via the CNC control of themachine, whereby the measuring devices constantly receive the actualvalues for the diameter of the main bearings I and IV. As soon as thetarget measurement has been attained at one of the main bearings of thecrankshaft 1, the grinding cycle is terminated and the grinding spindle12 moves out of the way.

Although FIG. 3 illustrates grinding of the main bearings on thecrankshaft 1, it is not possible for additional center sections of thecrankshaft 1 to be ground in the same clamp with a correspondinglymodified grinding wheel set.

FIG. 4 is a simplified side elevation of the top view illustrated inFIG. 3 in the region of the work area of the main bearing H:. As can beseen, the additional grinding device 11 with the grinding wheel 10 hasbeen pivoted upward; however, it is also conceivable that it can bepivoted in or out or driven into any other desired position depending onthe design of the grinding machine and the space available.

FIG. 5 illustrates in detail the grinding process with the grindingwheel 13 on the main bearing of the crankshaft 1, whereby the base bodyof the grinding wheel is labeled 13A and the CBN coating is labeled 14.In general, the coating height is approx. 5 mm. As can be seen, thelateral radii 15 on the main bearing of the crankshaft 1 are also groundin this case; For instance, a face shoulder height of approx. 4 to 5 mmis ground on the radius transition with respect to the face surfaces.

FIG. 6 is a simplified illustration of how grinding occurs on the mainbearing with the grinding wheel 13. The main bearing has an elevation 16that was created by preprocessing, for instance rotational milling orturning on a separate apparatus. It is plain to see that the grindingwheel 13 is only in grinding contact at the elevation 16 on this mainbearing, whereby however the lateral zones 17 and the other mainbearings of the crankshaft 1 are not also ground during grinding of thesteady seat. The steady is placed once grinding of the steady seat hasbegun on the circumference of the elevation 16.

Then the grinding wheel set is again moved into place so that thecrankshaft 1 can be ground to the finished final dimensions.

Legend

-   1 Crankshaft-   2 Main bearing I, II, III, IV-   3 Steady-   4, 5 Measuring device-   6 Chuck-   7 Longitudinal stop-   8, 9 Centering tips-   10 Grinding wheel-   11 Processing unit, additional grinding device-   12 Grinding spindle-   13 Grinding wheel-   14 Center axis-   15 Lateral radii-   16 Elevation-   17 Lateral zones

1. Apparatus for grinding center bearings of a crankshaft, comprising: aclamping unit for clamping and driving said crankshaft in an axis of itsrotation; a grinding spindle unit with a grinding spindle, said grindingspindle having an axis of rotation parallel to said axis of rotation ofsaid crankshaft, and said grinding spindle being positionableperpendicular to said crankshaft; a plurality of grinding wheels on saidgrinding spindle, corresponding to a number of center bearings to beground; a plurality of steadies, for supporting said crankshaft,opposite said grinding spindle, at least one of which supports saidcrankshaft in a region of at least one center bearing; and an additionalmachining unit for performing preliminary grinding on at least onecenter bearing, by forming an elevated bearing seat for said steadies,opposite said bearing, such that said steadies are continuously guidableduring grinding of said center bearings and provide counter-support. 2.Apparatus according to claim 1, wherein said additional machining unithas at least one grinding wheel.
 3. Apparatus according to claim 2,wherein said at least one grinding wheel of said additional machiningunit has a width that is less than a width of said center bearings. 4.Apparatus according to claim 2, wherein said at least one grinding wheelis a cubic boron nitride (CBN) grinding wheel.
 5. Apparatus according toclaim 1, wherein said additional machining unit alternatively isdriveable into and pivotable into contact with said crankshaft, betweensaid crankshaft and said grinding spindle, when said grinding spindle isin a non-contact position.
 6. Apparatus according to claim 5, wherein adrive for said additional machining unit is separate.
 7. Apparatusaccording to claim 1, wherein said steady is positionable at a centerbearing of said crankshaft.
 8. Method for grinding center bearings of acrankshaft, comprising simultaneously grinding said center bearings ofsaid crankshaft using a wheel set for the grinding of multiple bearings,wherein prior to a final grinding of said center bearings of saidcrankshaft to final dimensions, a bearing seat for a steady is ground onat least one said center bearing, said steady having differentdimensions from said final dimensions of said center bearings, andwherein said steady is guided during grinding of said bearing seat toits final dimensions.
 9. Method according to claim 8, wherein saidbearing seat is initially ground with a first grinding wheel; saidsteady is placed; and grinding of said center bearings of saidcrankshaft is completed using said grinding wheel set.
 10. Methodaccording to claim 8, wherein said bearing seat is initially ground witha grinding wheel of said grinding wheel set to an elevated contour of amain center bearing; said steady is placed; and grinding of said centerbearings of said crankshaft is completed.